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<title>Luminance HDR User Manual — Tonemapping operators reference — Fattal</title>
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<h2>Fattal</h2>

The implementation of a tone mapping operator as described in:
<P>
Gradient Domain High Dynamic Range Compression
R. Fattal, D. Lischinski, and M. Werman
In ACM Transactions on Graphics (3), p. 249, 2002.
<P>
With respect to the original paper, this program provides additional parameter
which limits the amplification of noise. The noise is often starkly amplified
because of division by zero in one of the equations in the paper. Extension
contributed by Przemyslaw Bazarnik.
<P>
At the core of the programme is a Poisson PDE which as suggested in
the original paper is solved using a Full Multigrid
Algorithm. However, this is an iterative solver which seems to lose
accuracy when applied to higher resolution images resulting in halo
effects and surreal looking images. For that reason a second solver
has been implemented using the discrete cosine transform as the
underlying method and is considerably more accurate mainly because it
is a direct solver. This solver is the preferred method and is used by
default. The old multigrid solver can be selected unchecking the <b>Version 2.3.0</b> checkbox.  
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<p>Please note that resulted LDR image always requires gamma correction which you can do using Levels tool.</p>

<H3>OPTIONS</H3>

<DL COMPACT>
<DT><B>Alpha</B><DD>
<P>
Set alpha parameter. This parameter is depreciated as setting a value other
than 1.0 has only the effect of a global gamma adjustment of the luminance
channel. 
See the paper for the definition of alpha. 
<DT><B>Beta</B><DD>
<P>
Set beta parameter. It sets the strength of gradient (local contrast) modification. 
Suggested range is 0.8 to 0.96, default is 0.9 (see paper for details). 
Value of 1 does not change contrasts, values above 1 reverse the effect: 
local contrast is stretched and details are attenuated.
Values below 0.5 lead to very strong amplification of small contrast, so
consider using <b>Noise Reduction</b> parameter to prevent noise.
<DT><B>Color Saturation</B><DD>
<P>
Amount of color saturation. Suggested range is 0.4 to 0.8. Default
value: 0.8.
<DT><B>Noise Reduction</B><DD>
<P>
Amount of noise reduction.
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